This invention relates to the formation of fibers from attenuable material and while the invention is adapted for use in the formation of fibers from a wide variety of attenuable materials, it is particularly suited to the attenuation of various thermoplastic materials, especially mineral materials such as glass and similar compositions which are rendered molten by heating. As with the technique of the prior applications above referred to, the present invention may be employed in connection not only with various mineral materials, but also with certain organic materials which are attenuable, such as polystyrene, polypropylene, polycarbonate and polyamides. Since the equipment or apparatus is especially useful in the attenuation of glass and similar thermoplastic materials, the following description refers to the use of glass by way of illustration.
Certain techniques for utilizing whirling currents or tornadoes for the attenuation of molten glass have been disclosed by us in prior applications above identified, such techniques being identified as toration. For example, U.S.A. Pat. No. 3,885,940, above identified, and also the companion U.S.A. Pat. No. 3,874,886, disclose development of pairs of counter-rotating tornadoes by directing a gaseous jet into a larger gaseous blast, thereby creating a zone of interaction including pairs of such tornadoes, and into which zone a stream of molten glass is delivered, with resultant attenuation of the glass stream.
In the equipment illustrated in said prior U.S.A. Pat. Nos. 3,885,940 and 3,874,886, the orifice from which the glass stream is delivered to the zone of interaction is located at or adjacent to the boundary of the blast. In our prior U.S. Pat. No. 4,015,954, toration arrangements are disclosed in which the glass orifice is positioned in spaced relation to the boundary of the blast, and in which the glass stream is delivered by gravity from an orifice spaced from the blast to the zone of interaction established by the interaction of a jet and a larger blast.
In prior applications Ser. Nos. 762,789, 676,755 and 780,589, both the glass orifices and the jet orifices are spaced from the boundary of the blast, and the glass streams are delivered to the jets and by the action of the jets are delivered into zones of interaction of the jets with the blast. In the applications just mentioned, the glass streams are also subjected to two stages of attenuation, one stage occuring in the jet and the other in the blast.
Still further in our application Ser. No. 762,789, the secondary or carrier jet which delivers the glass into the zone of interaction with the blast is caused to develop a stable zone of laminar flow lying between a pair of counter-rotating whirls or tornadoes formed in the jet flow upstream of the zone of penetration into the blast, and the glass stream is delivered to the laminar zone and thereafter enters the region of the tornadoes of the carrier jet, which latter merge downstream of the carrier jet, but before the carrier jet reaches the principal blast. As is pointed out in our application Ser. No. 762,789, the operation just described results in a two-stage attenuation, the first stage taking place as the glass stream is advanced into the influence of the tornadoes of the carrier jet, and the second stage taking place after the carrier jet and the partially attenuated stream enter the zone of interaction of the carrier jet with the blast.
According to the disclosure of said application Ser. No. 762,789, the zone of laminar flow and the tornadoes of the carrier jet are developed as a result of deflection of individual carrier jets provided for each fiberizing center and, as is brought out in said application Ser. No. 762,789 such deflection of a carrier jet contributes to stability of introduction of the glass into the system, notwithstanding the delivery of the glass to the carrier jet at a point spaced appreciably from the boundary of the principal blast.
The present invention, in common with application Ser. No. 762,789, has as a major objective, the stabilizing of the stream of glass or other attenuable material by development of a zone of laminar flow between tornadoes established in a jet flow system. However, the jet flow system of the present invention is somewhat different than that of said prior application, but it also provides various of the advantages thereof together with certain other advantages which are distinctive to the technique of the present invention.
In accordance with the present invention, jet guiding or deflecting means are employed at each fiberizing center. Instead of employing a jet deflector or baffle of the kind disclosed in application Ser. No. 762,789, the individual jets are each delivered into a concavely curved trough-like jet guiding device, conveniently in the form of a curved tube or elbow having the concave or inner wall removed, and the stream of attenuable material is introduced into the jet flow in the region where the inner wall of the tube has been removed. Thus, the stream of attenuable material is delivered to the jet in the region where the jet is flowing through the concavely curved trough-like guide.
Because of the guiding action of the sides of the trough-like portion of the guide and because of the induction of air or other ambient gas, each jet develops a pair of whirls or tornadoes, with a central generally laminar flow region lying between the tornadoes, and the stream of attenuable material is introduced into the zone of laminar flow between the tornadoes. In consequence, a preliminary attenuation of the stream of attenuable material is effected in the jet flow.
The invention also contemplates using the foregoing jet flow system in combination with a gaseous blast directed in a manner to intercept the jet and it is contemplated that the kinetic energy per unit of volume of the jet be greater than that of the blast and further that the cross sectional dimension of the jet be smaller than that of the blast in a direction transversely of the blast, so that the jet penetrates the blast and develops a zone of interaction between the jet and blast, which zone is of the type characterized by counter-rotating tornadoes, thereby providing for a second stage of attenuation, according to the toration type of technique more fully explained in the prior applications above referred to and also in the parent U.S. Pat. No. 3,885,940.
In the technique of the prior application Ser. No. 762,789, a series of jets are generated in a side-by-side relation and with a spacing sufficiently close to provide for impingement of the jets upon each other at least downstream of the edge of the deflector plate, so that the impingement of the jets upon each other aids in developing the counter-rotating tornadoes in pairs at opposite sides of a zone of substantially laminar flow. In contrast with the foregoing, in the system of the present invention, the pair of the tornadoes with the intervening zone of substantially laminar flow is generated without impingement of adjacent jets upon each other, in view of which according to the technique of the present invention any desired spacing of the jets may be adopted.
Because of the development of tornadoes in the curved guide element, the tornadoes of the pair developed in each jet have the same directions of rotation as the tornadoes in the zone of interaction of the jet flow with the blast. In view of this, any residual rotation of the tornadoes of the jets will reinforce the toration tornadoes in the zone of interaction of the jets with the blast.
The arrangement of the present invention as briefly described above, provides an effective technique for fiberizing attenuable material and in which each stream of attenuable material is preferably subjected to a two stage attenuation without, however, fragmenting the stream. The foregoing and various other objects and advantages will be brought out more fully hereinafter in the following detailed description of the invention in connection with the accompanying drawings.